This invention relates to internal combustion engines for propelling motor vehicles. More specifically it relates to control of exhaust gas recirculation, particularly during fueling transients.
Commonly owned U.S. Pat. No. 6,401,700 issued Jun. 11, 2002, discloses an engine control system that modifies exhaust gas recirculation (EGR) during fueling transients. A basic EGR rate is obtained from a map or table using current engine speed and current engine fueling. During a fueling transient the basic EGR rate is modified by an EGR transient multiplier, and the modified basic EGR rate is used instead of the basic EGR rate to control an EGR valve through which exhaust gas is recirculated. The value of the EGR transient multiplier is determined by a characteristic of the fueling transient, such as the severity of the transient.
The present invention relates to an improvement in EGR control strategy during fueling transients. Rather than utilizing only a characteristic of a fueling transient to determine how much the basic EGR rate should be modified during the transient, the invention introduces engine speed as an additional factor. By also using engine speed as a determinant of the extent to which the basic EGR rate should be modified during a fueling transient, it becomes possible to obtain better control over certain exhaust emissions over certain speed ranges. In particular, the invention can inhibit modification of the basic EGR rate at certain engine speeds without significant adverse consequences on some exhaust emission products, when certain fueling transients would otherwise be effective to modify the basic EGR rate in a manner that would cause increased generation of other exhaust emission products.
A specific example of the invention in one particular diesel engine inhibits modification of the basic EGR rate during fueling transients that, in the absence of engine speed as a factor, would modify the basic EGR rate when engine speed exceeds a selected speed, 2000 rpm in this example. In that diesel engine, the ability to inhibit modification of the basic EGR rate when the engine runs at relatively higher speeds can reduce the generation of oxides of nitrogen (NOx) without significant consequences on the generation of smoke at those speeds.
Principles of the invention are more encompassing than the example just given. There need not be merely an engine speed threshold above or below which the basic EGR rate is inhibited during a fueling transient. Rather, the rate can be inhibited whenever engine speed falls within one or more defined speed xe2x80x9cwindowsxe2x80x9d during a fueling transient, but otherwise not inhibited during a fueling transient. An example of this would be one that comprises a window at 2000-2400 rpm and a window at 2600-2800 rpm so that if a fueling transient were to occur while the engine was running at a speed within one of the windows, the basic EGR rate would be inhibited, but if the engine were running at any other speed when the fueling transient occurred, the basic EGR rate would not be inhibited.
Accordingly, one generic aspect of the present invention relates to an internal combustion engine comprising a control system comprising a processor for processing various data to develop data for control of engine fueling and of exhaust gas recirculation. The processor processes engine speed data and engine fueling data according to a function that correlates values of basic exhaust gas recirculation with values of engine speed and engine fueling to develop basic exhaust gas recirculation data. The processor processes engine speed data according to a function that correlates values of a speed-based modifier with values of engine speed to develop speed-based modifier data, and also processes engine fueling data to develop fueling transient data. The processor further processes the fueling transient data and the speed-based modifier data to develop speed-based fueling transient data, processes the speed-based fueling transient data according to a function that correlates values of a fueling transient modifier with values of speed-based fueling transient data to develop exhaust gas recirculation modifier data, and processes the exhaust gas recirculation modifier data and the basic exhaust gas recirculation data to develop modified exhaust gas recirculation data. The processor then causes exhaust gas to be recirculated in accordance with the modified exhaust gas recirculation data.
Another generic aspect relates to a method for modifying exhaust gas recirculation in an internal combustion engine during fueling transients. The method comprises: a) processing engine speed data and engine fueling data according to a function that correlates values of basic exhaust gas recirculation with values of engine speed and engine fueling to develop basic exhaust gas recirculation data, b) processing engine speed data according to a function that correlates values of a speed-based modifier with values of engine speed to develop speed-based modifier data, c) processing engine fueling data to develop fueling transient data, d) processing fueling transient data and speed-based modifier data to develop speed-based fueling transient data, e) processing speed-based fueling transient data according to a function that correlates values of a fueling transient modifier with values of fueling transient data to develop exhaust gas recirculation modifier data, f) processing the exhaust gas recirculation modifier data and basic exhaust gas recirculation data to develop modified exhaust gas recirculation data, and g) causing exhaust gas to be recirculated in accordance with the modified exhaust gas recirculation data.
Still other generic aspects relate to an internal combustion engine comprising a control system comprising a processor for processing various data to develop data for control of engine fueling and of exhaust gas recirculation, and to a corresponding method. The processor a) processes current engine speed data and current engine fueling data to develop basic exhaust gas recirculation data correlated with current engine speed and current engine fueling, b) processes current engine fueling data and current engine speed data to distinguish fueling transients that call for modification of the basic exhaust gas recirculation data, and c) when engine speed is within one selected speed range and the processing of engine fueling data and engine speed data discloses a fueling transient that calls for modification of the basic exhaust gas recirculation data, modifies the basic exhaust gas recirculation data by exhaust gas recirculation modifier data to develop modified exhaust gas recirculation data, and causes the modified exhaust gas recirculation data to control exhaust gas recirculation, and d) when engine speed is within another selected speed range and the processing of engine fueling data and engine speed data discloses a fueling transient that would otherwise call for modification of the basic exhaust gas recirculation data, inhibits modification of the basic exhaust gas recirculation data by exhaust gas recirculation modifier data, and causes the basic exhaust gas recirculation data to control exhaust gas recirculation.
The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, now briefly described as follows.